Vehicle systems, and aircraft system in particular, typically require execution of various diagnostic and operating tests upon system startup. For instance, when one Line Replaceable Unit (LRU) initiates operational tests on another isolated, hardware based, LRU or subassembly, a means to command a series of tests is necessary. Conventional aircraft systems utilize a binary-based bit interface system to facilitate diagnostic testing. For instance, a set of discrete or dedicated input/output (I/O) lines are employed with each I/O line assigned a respective binary value. Outputting a bit on a particular I/O line indicates a command to execute the corresponding diagnostic test.
If, for example, seven diagnostic tests are required upon system startup, a three-digit binary code is necessary to identify each diagnostic test (i.e., 000, 001, 010, . . . 111). Thus, the binary-based bit interface system requires three additional dedicated bit lines necessary to generate the three-digit binary code. However, as the number of required diagnostic test increases, the number binary values and the amount of I/O lines must also increase. Consequently, the number of components, the data lines, the weight, and the overall costs associated with conventional binary-based bit interface systems can increase exponentially as the number of required diagnostic tests increase.